1 /* 2 * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/vmSymbols.hpp" 27 #include "gc/shared/oopStorage.hpp" 28 #include "gc/shared/oopStorageSet.hpp" 29 #include "jfr/jfrEvents.hpp" 30 #include "jfr/support/jfrThreadId.hpp" 31 #include "logging/log.hpp" 32 #include "logging/logStream.hpp" 33 #include "memory/allocation.inline.hpp" 34 #include "memory/resourceArea.hpp" 35 #include "oops/markWord.hpp" 36 #include "oops/oop.inline.hpp" 37 #include "oops/oopHandle.inline.hpp" 38 #include "oops/weakHandle.inline.hpp" 39 #include "prims/jvmtiDeferredUpdates.hpp" 40 #include "prims/jvmtiExport.hpp" 41 #include "runtime/atomic.hpp" 42 #include "runtime/globals.hpp" 43 #include "runtime/handles.inline.hpp" 44 #include "runtime/interfaceSupport.inline.hpp" 45 #include "runtime/javaThread.inline.hpp" 46 #include "runtime/lightweightSynchronizer.hpp" 47 #include "runtime/mutexLocker.hpp" 48 #include "runtime/objectMonitor.hpp" 49 #include "runtime/objectMonitor.inline.hpp" 50 #include "runtime/orderAccess.hpp" 51 #include "runtime/osThread.hpp" 52 #include "runtime/perfData.hpp" 53 #include "runtime/safefetch.hpp" 54 #include "runtime/safepointMechanism.inline.hpp" 55 #include "runtime/sharedRuntime.hpp" 56 #include "runtime/synchronizer.hpp" 57 #include "services/threadService.hpp" 58 #include "utilities/debug.hpp" 59 #include "utilities/dtrace.hpp" 60 #include "utilities/globalDefinitions.hpp" 61 #include "utilities/macros.hpp" 62 #include "utilities/preserveException.hpp" 63 #if INCLUDE_JFR 64 #include "jfr/support/jfrFlush.hpp" 65 #endif 66 67 #ifdef DTRACE_ENABLED 68 69 // Only bother with this argument setup if dtrace is available 70 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 71 72 73 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 74 char* bytes = nullptr; \ 75 int len = 0; \ 76 jlong jtid = SharedRuntime::get_java_tid(thread); \ 77 Symbol* klassname = obj->klass()->name(); \ 78 if (klassname != nullptr) { \ 79 bytes = (char*)klassname->bytes(); \ 80 len = klassname->utf8_length(); \ 81 } 82 83 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 84 { \ 85 if (DTraceMonitorProbes) { \ 86 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 87 HOTSPOT_MONITOR_WAIT(jtid, \ 88 (monitor), bytes, len, (millis)); \ 89 } \ 90 } 91 92 #define HOTSPOT_MONITOR_contended__enter HOTSPOT_MONITOR_CONTENDED_ENTER 93 #define HOTSPOT_MONITOR_contended__entered HOTSPOT_MONITOR_CONTENDED_ENTERED 94 #define HOTSPOT_MONITOR_contended__exit HOTSPOT_MONITOR_CONTENDED_EXIT 95 #define HOTSPOT_MONITOR_notify HOTSPOT_MONITOR_NOTIFY 96 #define HOTSPOT_MONITOR_notifyAll HOTSPOT_MONITOR_NOTIFYALL 97 98 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 99 { \ 100 if (DTraceMonitorProbes) { \ 101 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 102 HOTSPOT_MONITOR_##probe(jtid, \ 103 (uintptr_t)(monitor), bytes, len); \ 104 } \ 105 } 106 107 #else // ndef DTRACE_ENABLED 108 109 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 110 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 111 112 #endif // ndef DTRACE_ENABLED 113 114 DEBUG_ONLY(static volatile bool InitDone = false;) 115 116 OopStorage* ObjectMonitor::_oop_storage = nullptr; 117 118 // ----------------------------------------------------------------------------- 119 // Theory of operations -- Monitors lists, thread residency, etc: 120 // 121 // * A thread acquires ownership of a monitor by successfully 122 // CAS()ing the _owner field from null to non-null. 123 // 124 // * Invariant: A thread appears on at most one monitor list -- 125 // cxq, EntryList or WaitSet -- at any one time. 126 // 127 // * Contending threads "push" themselves onto the cxq with CAS 128 // and then spin/park. 129 // 130 // * After a contending thread eventually acquires the lock it must 131 // dequeue itself from either the EntryList or the cxq. 132 // 133 // * The exiting thread identifies and unparks an "heir presumptive" 134 // tentative successor thread on the EntryList. Critically, the 135 // exiting thread doesn't unlink the successor thread from the EntryList. 136 // After having been unparked, the wakee will recontend for ownership of 137 // the monitor. The successor (wakee) will either acquire the lock or 138 // re-park itself. 139 // 140 // Succession is provided for by a policy of competitive handoff. 141 // The exiting thread does _not_ grant or pass ownership to the 142 // successor thread. (This is also referred to as "handoff" succession"). 143 // Instead the exiting thread releases ownership and possibly wakes 144 // a successor, so the successor can (re)compete for ownership of the lock. 145 // If the EntryList is empty but the cxq is populated the exiting 146 // thread will drain the cxq into the EntryList. It does so by 147 // by detaching the cxq (installing null with CAS) and folding 148 // the threads from the cxq into the EntryList. The EntryList is 149 // doubly linked, while the cxq is singly linked because of the 150 // CAS-based "push" used to enqueue recently arrived threads (RATs). 151 // 152 // * Concurrency invariants: 153 // 154 // -- only the monitor owner may access or mutate the EntryList. 155 // The mutex property of the monitor itself protects the EntryList 156 // from concurrent interference. 157 // -- Only the monitor owner may detach the cxq. 158 // 159 // * The monitor entry list operations avoid locks, but strictly speaking 160 // they're not lock-free. Enter is lock-free, exit is not. 161 // For a description of 'Methods and apparatus providing non-blocking access 162 // to a resource,' see U.S. Pat. No. 7844973. 163 // 164 // * The cxq can have multiple concurrent "pushers" but only one concurrent 165 // detaching thread. This mechanism is immune from the ABA corruption. 166 // More precisely, the CAS-based "push" onto cxq is ABA-oblivious. 167 // 168 // * Taken together, the cxq and the EntryList constitute or form a 169 // single logical queue of threads stalled trying to acquire the lock. 170 // We use two distinct lists to improve the odds of a constant-time 171 // dequeue operation after acquisition (in the ::enter() epilogue) and 172 // to reduce heat on the list ends. (c.f. Michael Scott's "2Q" algorithm). 173 // A key desideratum is to minimize queue & monitor metadata manipulation 174 // that occurs while holding the monitor lock -- that is, we want to 175 // minimize monitor lock holds times. Note that even a small amount of 176 // fixed spinning will greatly reduce the # of enqueue-dequeue operations 177 // on EntryList|cxq. That is, spinning relieves contention on the "inner" 178 // locks and monitor metadata. 179 // 180 // Cxq points to the set of Recently Arrived Threads attempting entry. 181 // Because we push threads onto _cxq with CAS, the RATs must take the form of 182 // a singly-linked LIFO. We drain _cxq into EntryList at unlock-time when 183 // the unlocking thread notices that EntryList is null but _cxq is != null. 184 // 185 // The EntryList is ordered by the prevailing queue discipline and 186 // can be organized in any convenient fashion, such as a doubly-linked list or 187 // a circular doubly-linked list. Critically, we want insert and delete operations 188 // to operate in constant-time. If we need a priority queue then something akin 189 // to Solaris' sleepq would work nicely. Viz., 190 // http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c. 191 // Queue discipline is enforced at ::exit() time, when the unlocking thread 192 // drains the cxq into the EntryList, and orders or reorders the threads on the 193 // EntryList accordingly. 194 // 195 // Barring "lock barging", this mechanism provides fair cyclic ordering, 196 // somewhat similar to an elevator-scan. 197 // 198 // * The monitor synchronization subsystem avoids the use of native 199 // synchronization primitives except for the narrow platform-specific 200 // park-unpark abstraction. See the comments in os_solaris.cpp regarding 201 // the semantics of park-unpark. Put another way, this monitor implementation 202 // depends only on atomic operations and park-unpark. The monitor subsystem 203 // manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the 204 // underlying OS manages the READY<->RUN transitions. 205 // 206 // * Waiting threads reside on the WaitSet list -- wait() puts 207 // the caller onto the WaitSet. 208 // 209 // * notify() or notifyAll() simply transfers threads from the WaitSet to 210 // either the EntryList or cxq. Subsequent exit() operations will 211 // unpark the notifyee. Unparking a notifee in notify() is inefficient - 212 // it's likely the notifyee would simply impale itself on the lock held 213 // by the notifier. 214 // 215 // * An interesting alternative is to encode cxq as (List,LockByte) where 216 // the LockByte is 0 iff the monitor is owned. _owner is simply an auxiliary 217 // variable, like _recursions, in the scheme. The threads or Events that form 218 // the list would have to be aligned in 256-byte addresses. A thread would 219 // try to acquire the lock or enqueue itself with CAS, but exiting threads 220 // could use a 1-0 protocol and simply STB to set the LockByte to 0. 221 // Note that is is *not* word-tearing, but it does presume that full-word 222 // CAS operations are coherent with intermix with STB operations. That's true 223 // on most common processors. 224 // 225 // * See also http://blogs.sun.com/dave 226 227 228 // Check that object() and set_object() are called from the right context: 229 static void check_object_context() { 230 #ifdef ASSERT 231 Thread* self = Thread::current(); 232 if (self->is_Java_thread()) { 233 // Mostly called from JavaThreads so sanity check the thread state. 234 JavaThread* jt = JavaThread::cast(self); 235 switch (jt->thread_state()) { 236 case _thread_in_vm: // the usual case 237 case _thread_in_Java: // during deopt 238 break; 239 default: 240 fatal("called from an unsafe thread state"); 241 } 242 assert(jt->is_active_Java_thread(), "must be active JavaThread"); 243 } else { 244 // However, ThreadService::get_current_contended_monitor() 245 // can call here via the VMThread so sanity check it. 246 assert(self->is_VM_thread(), "must be"); 247 } 248 #endif // ASSERT 249 } 250 251 ObjectMonitor::ObjectMonitor(oop object) : 252 _metadata(0), 253 _object(_oop_storage, object), 254 _owner(nullptr), 255 _previous_owner_tid(0), 256 _next_om(nullptr), 257 _recursions(0), 258 _EntryList(nullptr), 259 _cxq(nullptr), 260 _succ(nullptr), 261 _Responsible(nullptr), 262 _SpinDuration(ObjectMonitor::Knob_SpinLimit), 263 _contentions(0), 264 _WaitSet(nullptr), 265 _waiters(0), 266 _WaitSetLock(0) 267 { } 268 269 ObjectMonitor::~ObjectMonitor() { 270 _object.release(_oop_storage); 271 } 272 273 oop ObjectMonitor::object() const { 274 check_object_context(); 275 return _object.resolve(); 276 } 277 278 void ObjectMonitor::ExitOnSuspend::operator()(JavaThread* current) { 279 if (current->is_suspended()) { 280 _om->_recursions = 0; 281 _om->_succ = nullptr; 282 // Don't need a full fence after clearing successor here because of the call to exit(). 283 _om->exit(current, false /* not_suspended */); 284 _om_exited = true; 285 286 current->set_current_pending_monitor(_om); 287 } 288 } 289 290 void ObjectMonitor::ClearSuccOnSuspend::operator()(JavaThread* current) { 291 if (current->is_suspended()) { 292 if (_om->_succ == current) { 293 _om->_succ = nullptr; 294 OrderAccess::fence(); // always do a full fence when successor is cleared 295 } 296 } 297 } 298 299 #define assert_mark_word_consistency() \ 300 assert(UseObjectMonitorTable || object()->mark() == markWord::encode(this), \ 301 "object mark must match encoded this: mark=" INTPTR_FORMAT \ 302 ", encoded this=" INTPTR_FORMAT, object()->mark().value(), \ 303 markWord::encode(this).value()); 304 305 // ----------------------------------------------------------------------------- 306 // Enter support 307 308 bool ObjectMonitor::enter_is_async_deflating() { 309 if (is_being_async_deflated()) { 310 if (!UseObjectMonitorTable) { 311 const oop l_object = object(); 312 if (l_object != nullptr) { 313 // Attempt to restore the header/dmw to the object's header so that 314 // we only retry once if the deflater thread happens to be slow. 315 install_displaced_markword_in_object(l_object); 316 } 317 } 318 return true; 319 } 320 321 return false; 322 } 323 324 void ObjectMonitor::enter_for_with_contention_mark(JavaThread* locking_thread, ObjectMonitorContentionMark& contention_mark) { 325 // Used by ObjectSynchronizer::enter_for to enter for another thread. 326 // The monitor is private to or already owned by locking_thread which must be suspended. 327 // So this code may only contend with deflation. 328 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be"); 329 assert(contention_mark._monitor == this, "must be"); 330 assert(!is_being_async_deflated(), "must be"); 331 332 333 void* prev_owner = try_set_owner_from(nullptr, locking_thread); 334 335 bool success = false; 336 337 if (prev_owner == nullptr) { 338 assert(_recursions == 0, "invariant"); 339 success = true; 340 } else if (prev_owner == locking_thread) { 341 _recursions++; 342 success = true; 343 } else if (prev_owner == DEFLATER_MARKER) { 344 // Racing with deflation. 345 prev_owner = try_set_owner_from(DEFLATER_MARKER, locking_thread); 346 if (prev_owner == DEFLATER_MARKER) { 347 // Cancelled deflation. Increment contentions as part of the deflation protocol. 348 add_to_contentions(1); 349 success = true; 350 } else if (prev_owner == nullptr) { 351 // At this point we cannot race with deflation as we have both incremented 352 // contentions, seen contention > 0 and seen a DEFLATER_MARKER. 353 // success will only be false if this races with something other than 354 // deflation. 355 prev_owner = try_set_owner_from(nullptr, locking_thread); 356 success = prev_owner == nullptr; 357 } 358 } else if (LockingMode == LM_LEGACY && locking_thread->is_lock_owned((address)prev_owner)) { 359 assert(_recursions == 0, "must be"); 360 _recursions = 1; 361 set_owner_from_BasicLock(prev_owner, locking_thread); 362 success = true; 363 } 364 assert(success, "Failed to enter_for: locking_thread=" INTPTR_FORMAT 365 ", this=" INTPTR_FORMAT "{owner=" INTPTR_FORMAT "}, observed owner: " INTPTR_FORMAT, 366 p2i(locking_thread), p2i(this), p2i(owner_raw()), p2i(prev_owner)); 367 } 368 369 bool ObjectMonitor::enter_for(JavaThread* locking_thread) { 370 371 // Block out deflation as soon as possible. 372 ObjectMonitorContentionMark contention_mark(this); 373 374 // Check for deflation. 375 if (enter_is_async_deflating()) { 376 return false; 377 } 378 379 enter_for_with_contention_mark(locking_thread, contention_mark); 380 assert(owner_raw() == locking_thread, "must be"); 381 return true; 382 } 383 384 bool ObjectMonitor::try_enter(JavaThread* current) { 385 // TryLock avoids the CAS 386 TryLockResult r = TryLock(current); 387 if (r == TryLockResult::Success) { 388 assert(_recursions == 0, "invariant"); 389 return true; 390 } 391 392 if (r == TryLockResult::HasOwner && owner() == current) { 393 _recursions++; 394 return true; 395 } 396 397 void* cur = owner_raw(); 398 if (LockingMode == LM_LEGACY && current->is_lock_owned((address)cur)) { 399 assert(_recursions == 0, "internal state error"); 400 _recursions = 1; 401 set_owner_from_BasicLock(cur, current); // Convert from BasicLock* to Thread*. 402 return true; 403 } 404 405 return false; 406 } 407 408 bool ObjectMonitor::spin_enter(JavaThread* current) { 409 assert(current == JavaThread::current(), "must be"); 410 411 // Check for recursion. 412 if (try_enter(current)) { 413 return true; 414 } 415 416 // Check for deflation. 417 if (enter_is_async_deflating()) { 418 return false; 419 } 420 421 // We've encountered genuine contention. 422 423 // Do one round of spinning. 424 // Note that if we acquire the monitor from an initial spin 425 // we forgo posting JVMTI events and firing DTRACE probes. 426 if (TrySpin(current)) { 427 assert(owner_raw() == current, "must be current: owner=" INTPTR_FORMAT, p2i(owner_raw())); 428 assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions); 429 assert_mark_word_consistency(); 430 return true; 431 } 432 433 return false; 434 } 435 436 bool ObjectMonitor::enter(JavaThread* current) { 437 assert(current == JavaThread::current(), "must be"); 438 439 if (spin_enter(current)) { 440 return true; 441 } 442 443 assert(owner_raw() != current, "invariant"); 444 assert(_succ != current, "invariant"); 445 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 446 assert(current->thread_state() != _thread_blocked, "invariant"); 447 448 // Keep is_being_async_deflated stable across the rest of enter 449 ObjectMonitorContentionMark contention_mark(this); 450 451 // Check for deflation. 452 if (enter_is_async_deflating()) { 453 return false; 454 } 455 456 // At this point this ObjectMonitor cannot be deflated, finish contended enter 457 enter_with_contention_mark(current, contention_mark); 458 return true; 459 } 460 461 void ObjectMonitor::enter_with_contention_mark(JavaThread *current, ObjectMonitorContentionMark &cm) { 462 assert(current == JavaThread::current(), "must be"); 463 assert(owner_raw() != current, "must be"); 464 assert(cm._monitor == this, "must be"); 465 assert(!is_being_async_deflated(), "must be"); 466 467 JFR_ONLY(JfrConditionalFlush<EventJavaMonitorEnter> flush(current);) 468 EventJavaMonitorEnter event; 469 if (event.is_started()) { 470 event.set_monitorClass(object()->klass()); 471 // Set an address that is 'unique enough', such that events close in 472 // time and with the same address are likely (but not guaranteed) to 473 // belong to the same object. 474 event.set_address((uintptr_t)this); 475 } 476 477 { // Change java thread status to indicate blocked on monitor enter. 478 JavaThreadBlockedOnMonitorEnterState jtbmes(current, this); 479 480 assert(current->current_pending_monitor() == nullptr, "invariant"); 481 current->set_current_pending_monitor(this); 482 483 DTRACE_MONITOR_PROBE(contended__enter, this, object(), current); 484 if (JvmtiExport::should_post_monitor_contended_enter()) { 485 JvmtiExport::post_monitor_contended_enter(current, this); 486 487 // The current thread does not yet own the monitor and does not 488 // yet appear on any queues that would get it made the successor. 489 // This means that the JVMTI_EVENT_MONITOR_CONTENDED_ENTER event 490 // handler cannot accidentally consume an unpark() meant for the 491 // ParkEvent associated with this ObjectMonitor. 492 } 493 494 OSThreadContendState osts(current->osthread()); 495 496 assert(current->thread_state() == _thread_in_vm, "invariant"); 497 498 for (;;) { 499 ExitOnSuspend eos(this); 500 { 501 ThreadBlockInVMPreprocess<ExitOnSuspend> tbivs(current, eos, true /* allow_suspend */); 502 EnterI(current); 503 current->set_current_pending_monitor(nullptr); 504 // We can go to a safepoint at the end of this block. If we 505 // do a thread dump during that safepoint, then this thread will show 506 // as having "-locked" the monitor, but the OS and java.lang.Thread 507 // states will still report that the thread is blocked trying to 508 // acquire it. 509 // If there is a suspend request, ExitOnSuspend will exit the OM 510 // and set the OM as pending. 511 } 512 if (!eos.exited()) { 513 // ExitOnSuspend did not exit the OM 514 assert(owner_raw() == current, "invariant"); 515 break; 516 } 517 } 518 519 // We've just gotten past the enter-check-for-suspend dance and we now own 520 // the monitor free and clear. 521 } 522 523 assert(contentions() >= 0, "must not be negative: contentions=%d", contentions()); 524 525 // Must either set _recursions = 0 or ASSERT _recursions == 0. 526 assert(_recursions == 0, "invariant"); 527 assert(owner_raw() == current, "invariant"); 528 assert(_succ != current, "invariant"); 529 assert_mark_word_consistency(); 530 531 // The thread -- now the owner -- is back in vm mode. 532 // Report the glorious news via TI,DTrace and jvmstat. 533 // The probe effect is non-trivial. All the reportage occurs 534 // while we hold the monitor, increasing the length of the critical 535 // section. Amdahl's parallel speedup law comes vividly into play. 536 // 537 // Another option might be to aggregate the events (thread local or 538 // per-monitor aggregation) and defer reporting until a more opportune 539 // time -- such as next time some thread encounters contention but has 540 // yet to acquire the lock. While spinning that thread could 541 // spinning we could increment JVMStat counters, etc. 542 543 DTRACE_MONITOR_PROBE(contended__entered, this, object(), current); 544 if (JvmtiExport::should_post_monitor_contended_entered()) { 545 JvmtiExport::post_monitor_contended_entered(current, this); 546 547 // The current thread already owns the monitor and is not going to 548 // call park() for the remainder of the monitor enter protocol. So 549 // it doesn't matter if the JVMTI_EVENT_MONITOR_CONTENDED_ENTERED 550 // event handler consumed an unpark() issued by the thread that 551 // just exited the monitor. 552 } 553 if (event.should_commit()) { 554 event.set_previousOwner(_previous_owner_tid); 555 event.commit(); 556 } 557 OM_PERFDATA_OP(ContendedLockAttempts, inc()); 558 } 559 560 // Caveat: TryLock() is not necessarily serializing if it returns failure. 561 // Callers must compensate as needed. 562 563 ObjectMonitor::TryLockResult ObjectMonitor::TryLock(JavaThread* current) { 564 void* own = owner_raw(); 565 if (own != nullptr) return TryLockResult::HasOwner; 566 if (try_set_owner_from(nullptr, current) == nullptr) { 567 assert(_recursions == 0, "invariant"); 568 return TryLockResult::Success; 569 } 570 // The lock had been free momentarily, but we lost the race to the lock. 571 // Interference -- the CAS failed. 572 // We can either return -1 or retry. 573 // Retry doesn't make as much sense because the lock was just acquired. 574 return TryLockResult::Interference; 575 } 576 577 // Deflate the specified ObjectMonitor if not in-use. Returns true if it 578 // was deflated and false otherwise. 579 // 580 // The async deflation protocol sets owner to DEFLATER_MARKER and 581 // makes contentions negative as signals to contending threads that 582 // an async deflation is in progress. There are a number of checks 583 // as part of the protocol to make sure that the calling thread has 584 // not lost the race to a contending thread. 585 // 586 // The ObjectMonitor has been successfully async deflated when: 587 // (contentions < 0) 588 // Contending threads that see that condition know to retry their operation. 589 // 590 bool ObjectMonitor::deflate_monitor(Thread* current) { 591 if (is_busy()) { 592 // Easy checks are first - the ObjectMonitor is busy so no deflation. 593 return false; 594 } 595 596 const oop obj = object_peek(); 597 598 if (obj == nullptr) { 599 // If the object died, we can recycle the monitor without racing with 600 // Java threads. The GC already broke the association with the object. 601 set_owner_from(nullptr, DEFLATER_MARKER); 602 assert(contentions() >= 0, "must be non-negative: contentions=%d", contentions()); 603 _contentions = INT_MIN; // minimum negative int 604 } else { 605 // Attempt async deflation protocol. 606 607 // Set a null owner to DEFLATER_MARKER to force any contending thread 608 // through the slow path. This is just the first part of the async 609 // deflation dance. 610 if (try_set_owner_from(nullptr, DEFLATER_MARKER) != nullptr) { 611 // The owner field is no longer null so we lost the race since the 612 // ObjectMonitor is now busy. 613 return false; 614 } 615 616 if (contentions() > 0 || _waiters != 0) { 617 // Another thread has raced to enter the ObjectMonitor after 618 // is_busy() above or has already entered and waited on 619 // it which makes it busy so no deflation. Restore owner to 620 // null if it is still DEFLATER_MARKER. 621 if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) { 622 // Deferred decrement for the JT EnterI() that cancelled the async deflation. 623 add_to_contentions(-1); 624 } 625 return false; 626 } 627 628 // Make a zero contentions field negative to force any contending threads 629 // to retry. This is the second part of the async deflation dance. 630 if (Atomic::cmpxchg(&_contentions, 0, INT_MIN) != 0) { 631 // Contentions was no longer 0 so we lost the race since the 632 // ObjectMonitor is now busy. Restore owner to null if it is 633 // still DEFLATER_MARKER: 634 if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) { 635 // Deferred decrement for the JT EnterI() that cancelled the async deflation. 636 add_to_contentions(-1); 637 } 638 return false; 639 } 640 } 641 642 // Sanity checks for the races: 643 guarantee(owner_is_DEFLATER_MARKER(), "must be deflater marker"); 644 guarantee(contentions() < 0, "must be negative: contentions=%d", 645 contentions()); 646 guarantee(_waiters == 0, "must be 0: waiters=%d", _waiters); 647 guarantee(_cxq == nullptr, "must be no contending threads: cxq=" 648 INTPTR_FORMAT, p2i(_cxq)); 649 guarantee(_EntryList == nullptr, 650 "must be no entering threads: EntryList=" INTPTR_FORMAT, 651 p2i(_EntryList)); 652 653 if (obj != nullptr) { 654 if (log_is_enabled(Trace, monitorinflation)) { 655 ResourceMark rm; 656 log_trace(monitorinflation)("deflate_monitor: object=" INTPTR_FORMAT 657 ", mark=" INTPTR_FORMAT ", type='%s'", 658 p2i(obj), obj->mark().value(), 659 obj->klass()->external_name()); 660 } 661 } 662 663 if (UseObjectMonitorTable) { 664 LightweightSynchronizer::deflate_monitor(current, obj, this); 665 } else { 666 if (obj != nullptr) { 667 // Install the old mark word if nobody else has already done it. 668 install_displaced_markword_in_object(obj); 669 } 670 } 671 672 // We leave owner == DEFLATER_MARKER and contentions < 0 673 // to force any racing threads to retry. 674 return true; // Success, ObjectMonitor has been deflated. 675 } 676 677 // Install the displaced mark word (dmw) of a deflating ObjectMonitor 678 // into the header of the object associated with the monitor. This 679 // idempotent method is called by a thread that is deflating a 680 // monitor and by other threads that have detected a race with the 681 // deflation process. 682 void ObjectMonitor::install_displaced_markword_in_object(const oop obj) { 683 assert(!UseObjectMonitorTable, "Lightweight has no dmw"); 684 // This function must only be called when (owner == DEFLATER_MARKER 685 // && contentions <= 0), but we can't guarantee that here because 686 // those values could change when the ObjectMonitor gets moved from 687 // the global free list to a per-thread free list. 688 689 guarantee(obj != nullptr, "must be non-null"); 690 691 // Separate loads in is_being_async_deflated(), which is almost always 692 // called before this function, from the load of dmw/header below. 693 694 // _contentions and dmw/header may get written by different threads. 695 // Make sure to observe them in the same order when having several observers. 696 OrderAccess::loadload_for_IRIW(); 697 698 const oop l_object = object_peek(); 699 if (l_object == nullptr) { 700 // ObjectMonitor's object ref has already been cleared by async 701 // deflation or GC so we're done here. 702 return; 703 } 704 assert(l_object == obj, "object=" INTPTR_FORMAT " must equal obj=" 705 INTPTR_FORMAT, p2i(l_object), p2i(obj)); 706 707 markWord dmw = header(); 708 // The dmw has to be neutral (not null, not locked and not marked). 709 assert(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value()); 710 711 // Install displaced mark word if the object's header still points 712 // to this ObjectMonitor. More than one racing caller to this function 713 // can rarely reach this point, but only one can win. 714 markWord res = obj->cas_set_mark(dmw, markWord::encode(this)); 715 if (res != markWord::encode(this)) { 716 // This should be rare so log at the Info level when it happens. 717 log_info(monitorinflation)("install_displaced_markword_in_object: " 718 "failed cas_set_mark: new_mark=" INTPTR_FORMAT 719 ", old_mark=" INTPTR_FORMAT ", res=" INTPTR_FORMAT, 720 dmw.value(), markWord::encode(this).value(), 721 res.value()); 722 } 723 724 // Note: It does not matter which thread restored the header/dmw 725 // into the object's header. The thread deflating the monitor just 726 // wanted the object's header restored and it is. The threads that 727 // detected a race with the deflation process also wanted the 728 // object's header restored before they retry their operation and 729 // because it is restored they will only retry once. 730 } 731 732 // Convert the fields used by is_busy() to a string that can be 733 // used for diagnostic output. 734 const char* ObjectMonitor::is_busy_to_string(stringStream* ss) { 735 ss->print("is_busy: waiters=%d" 736 ", contentions=%d" 737 ", owner=" PTR_FORMAT 738 ", cxq=" PTR_FORMAT 739 ", EntryList=" PTR_FORMAT, 740 _waiters, 741 (contentions() > 0 ? contentions() : 0), 742 owner_is_DEFLATER_MARKER() 743 // We report null instead of DEFLATER_MARKER here because is_busy() 744 // ignores DEFLATER_MARKER values. 745 ? p2i(nullptr) 746 : p2i(owner_raw()), 747 p2i(_cxq), 748 p2i(_EntryList)); 749 return ss->base(); 750 } 751 752 #define MAX_RECHECK_INTERVAL 1000 753 754 void ObjectMonitor::EnterI(JavaThread* current) { 755 assert(current->thread_state() == _thread_blocked, "invariant"); 756 757 // Try the lock - TATAS 758 if (TryLock(current) == TryLockResult::Success) { 759 assert(_succ != current, "invariant"); 760 assert(owner_raw() == current, "invariant"); 761 assert(_Responsible != current, "invariant"); 762 return; 763 } 764 765 if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) { 766 // Cancelled the in-progress async deflation by changing owner from 767 // DEFLATER_MARKER to current. As part of the contended enter protocol, 768 // contentions was incremented to a positive value before EnterI() 769 // was called and that prevents the deflater thread from winning the 770 // last part of the 2-part async deflation protocol. After EnterI() 771 // returns to enter(), contentions is decremented because the caller 772 // now owns the monitor. We bump contentions an extra time here to 773 // prevent the deflater thread from winning the last part of the 774 // 2-part async deflation protocol after the regular decrement 775 // occurs in enter(). The deflater thread will decrement contentions 776 // after it recognizes that the async deflation was cancelled. 777 add_to_contentions(1); 778 assert(_succ != current, "invariant"); 779 assert(_Responsible != current, "invariant"); 780 return; 781 } 782 783 assert(InitDone, "Unexpectedly not initialized"); 784 785 // We try one round of spinning *before* enqueueing current. 786 // 787 // If the _owner is ready but OFFPROC we could use a YieldTo() 788 // operation to donate the remainder of this thread's quantum 789 // to the owner. This has subtle but beneficial affinity 790 // effects. 791 792 if (TrySpin(current)) { 793 assert(owner_raw() == current, "invariant"); 794 assert(_succ != current, "invariant"); 795 assert(_Responsible != current, "invariant"); 796 return; 797 } 798 799 // The Spin failed -- Enqueue and park the thread ... 800 assert(_succ != current, "invariant"); 801 assert(owner_raw() != current, "invariant"); 802 assert(_Responsible != current, "invariant"); 803 804 // Enqueue "current" on ObjectMonitor's _cxq. 805 // 806 // Node acts as a proxy for current. 807 // As an aside, if were to ever rewrite the synchronization code mostly 808 // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class 809 // Java objects. This would avoid awkward lifecycle and liveness issues, 810 // as well as eliminate a subset of ABA issues. 811 // TODO: eliminate ObjectWaiter and enqueue either Threads or Events. 812 813 ObjectWaiter node(current); 814 current->_ParkEvent->reset(); 815 node._prev = (ObjectWaiter*) 0xBAD; 816 node.TState = ObjectWaiter::TS_CXQ; 817 818 // Push "current" onto the front of the _cxq. 819 // Once on cxq/EntryList, current stays on-queue until it acquires the lock. 820 // Note that spinning tends to reduce the rate at which threads 821 // enqueue and dequeue on EntryList|cxq. 822 ObjectWaiter* nxt; 823 for (;;) { 824 node._next = nxt = _cxq; 825 if (Atomic::cmpxchg(&_cxq, nxt, &node) == nxt) break; 826 827 // Interference - the CAS failed because _cxq changed. Just retry. 828 // As an optional optimization we retry the lock. 829 if (TryLock(current) == TryLockResult::Success) { 830 assert(_succ != current, "invariant"); 831 assert(owner_raw() == current, "invariant"); 832 assert(_Responsible != current, "invariant"); 833 return; 834 } 835 } 836 837 // Check for cxq|EntryList edge transition to non-null. This indicates 838 // the onset of contention. While contention persists exiting threads 839 // will use a ST:MEMBAR:LD 1-1 exit protocol. When contention abates exit 840 // operations revert to the faster 1-0 mode. This enter operation may interleave 841 // (race) a concurrent 1-0 exit operation, resulting in stranding, so we 842 // arrange for one of the contending thread to use a timed park() operations 843 // to detect and recover from the race. (Stranding is form of progress failure 844 // where the monitor is unlocked but all the contending threads remain parked). 845 // That is, at least one of the contended threads will periodically poll _owner. 846 // One of the contending threads will become the designated "Responsible" thread. 847 // The Responsible thread uses a timed park instead of a normal indefinite park 848 // operation -- it periodically wakes and checks for and recovers from potential 849 // strandings admitted by 1-0 exit operations. We need at most one Responsible 850 // thread per-monitor at any given moment. Only threads on cxq|EntryList may 851 // be responsible for a monitor. 852 // 853 // Currently, one of the contended threads takes on the added role of "Responsible". 854 // A viable alternative would be to use a dedicated "stranding checker" thread 855 // that periodically iterated over all the threads (or active monitors) and unparked 856 // successors where there was risk of stranding. This would help eliminate the 857 // timer scalability issues we see on some platforms as we'd only have one thread 858 // -- the checker -- parked on a timer. 859 860 if (nxt == nullptr && _EntryList == nullptr) { 861 // Try to assume the role of responsible thread for the monitor. 862 // CONSIDER: ST vs CAS vs { if (Responsible==null) Responsible=current } 863 Atomic::replace_if_null(&_Responsible, current); 864 } 865 866 // The lock might have been released while this thread was occupied queueing 867 // itself onto _cxq. To close the race and avoid "stranding" and 868 // progress-liveness failure we must resample-retry _owner before parking. 869 // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner. 870 // In this case the ST-MEMBAR is accomplished with CAS(). 871 // 872 // TODO: Defer all thread state transitions until park-time. 873 // Since state transitions are heavy and inefficient we'd like 874 // to defer the state transitions until absolutely necessary, 875 // and in doing so avoid some transitions ... 876 877 int recheckInterval = 1; 878 879 for (;;) { 880 881 if (TryLock(current) == TryLockResult::Success) { 882 break; 883 } 884 assert(owner_raw() != current, "invariant"); 885 886 // park self 887 if (_Responsible == current) { 888 current->_ParkEvent->park((jlong) recheckInterval); 889 // Increase the recheckInterval, but clamp the value. 890 recheckInterval *= 8; 891 if (recheckInterval > MAX_RECHECK_INTERVAL) { 892 recheckInterval = MAX_RECHECK_INTERVAL; 893 } 894 } else { 895 current->_ParkEvent->park(); 896 } 897 898 if (TryLock(current) == TryLockResult::Success) { 899 break; 900 } 901 902 if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) { 903 // Cancelled the in-progress async deflation by changing owner from 904 // DEFLATER_MARKER to current. As part of the contended enter protocol, 905 // contentions was incremented to a positive value before EnterI() 906 // was called and that prevents the deflater thread from winning the 907 // last part of the 2-part async deflation protocol. After EnterI() 908 // returns to enter(), contentions is decremented because the caller 909 // now owns the monitor. We bump contentions an extra time here to 910 // prevent the deflater thread from winning the last part of the 911 // 2-part async deflation protocol after the regular decrement 912 // occurs in enter(). The deflater thread will decrement contentions 913 // after it recognizes that the async deflation was cancelled. 914 add_to_contentions(1); 915 break; 916 } 917 918 // The lock is still contested. 919 920 // Keep a tally of the # of futile wakeups. 921 // Note that the counter is not protected by a lock or updated by atomics. 922 // That is by design - we trade "lossy" counters which are exposed to 923 // races during updates for a lower probe effect. 924 // This PerfData object can be used in parallel with a safepoint. 925 // See the work around in PerfDataManager::destroy(). 926 OM_PERFDATA_OP(FutileWakeups, inc()); 927 928 // Assuming this is not a spurious wakeup we'll normally find _succ == current. 929 // We can defer clearing _succ until after the spin completes 930 // TrySpin() must tolerate being called with _succ == current. 931 // Try yet another round of adaptive spinning. 932 if (TrySpin(current)) { 933 break; 934 } 935 936 // We can find that we were unpark()ed and redesignated _succ while 937 // we were spinning. That's harmless. If we iterate and call park(), 938 // park() will consume the event and return immediately and we'll 939 // just spin again. This pattern can repeat, leaving _succ to simply 940 // spin on a CPU. 941 942 if (_succ == current) _succ = nullptr; 943 944 // Invariant: after clearing _succ a thread *must* retry _owner before parking. 945 OrderAccess::fence(); 946 } 947 948 // Egress : 949 // current has acquired the lock -- Unlink current from the cxq or EntryList. 950 // Normally we'll find current on the EntryList . 951 // From the perspective of the lock owner (this thread), the 952 // EntryList is stable and cxq is prepend-only. 953 // The head of cxq is volatile but the interior is stable. 954 // In addition, current.TState is stable. 955 956 assert(owner_raw() == current, "invariant"); 957 958 UnlinkAfterAcquire(current, &node); 959 if (_succ == current) _succ = nullptr; 960 961 assert(_succ != current, "invariant"); 962 if (_Responsible == current) { 963 _Responsible = nullptr; 964 OrderAccess::fence(); // Dekker pivot-point 965 966 // We may leave threads on cxq|EntryList without a designated 967 // "Responsible" thread. This is benign. When this thread subsequently 968 // exits the monitor it can "see" such preexisting "old" threads -- 969 // threads that arrived on the cxq|EntryList before the fence, above -- 970 // by LDing cxq|EntryList. Newly arrived threads -- that is, threads 971 // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible 972 // non-null and elect a new "Responsible" timer thread. 973 // 974 // This thread executes: 975 // ST Responsible=null; MEMBAR (in enter epilogue - here) 976 // LD cxq|EntryList (in subsequent exit) 977 // 978 // Entering threads in the slow/contended path execute: 979 // ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog) 980 // The (ST cxq; MEMBAR) is accomplished with CAS(). 981 // 982 // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent 983 // exit operation from floating above the ST Responsible=null. 984 } 985 986 // We've acquired ownership with CAS(). 987 // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics. 988 // But since the CAS() this thread may have also stored into _succ, 989 // EntryList, cxq or Responsible. These meta-data updates must be 990 // visible __before this thread subsequently drops the lock. 991 // Consider what could occur if we didn't enforce this constraint -- 992 // STs to monitor meta-data and user-data could reorder with (become 993 // visible after) the ST in exit that drops ownership of the lock. 994 // Some other thread could then acquire the lock, but observe inconsistent 995 // or old monitor meta-data and heap data. That violates the JMM. 996 // To that end, the 1-0 exit() operation must have at least STST|LDST 997 // "release" barrier semantics. Specifically, there must be at least a 998 // STST|LDST barrier in exit() before the ST of null into _owner that drops 999 // the lock. The barrier ensures that changes to monitor meta-data and data 1000 // protected by the lock will be visible before we release the lock, and 1001 // therefore before some other thread (CPU) has a chance to acquire the lock. 1002 // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html. 1003 // 1004 // Critically, any prior STs to _succ or EntryList must be visible before 1005 // the ST of null into _owner in the *subsequent* (following) corresponding 1006 // monitorexit. Recall too, that in 1-0 mode monitorexit does not necessarily 1007 // execute a serializing instruction. 1008 1009 return; 1010 } 1011 1012 // ReenterI() is a specialized inline form of the latter half of the 1013 // contended slow-path from EnterI(). We use ReenterI() only for 1014 // monitor reentry in wait(). 1015 // 1016 // In the future we should reconcile EnterI() and ReenterI(). 1017 1018 void ObjectMonitor::ReenterI(JavaThread* current, ObjectWaiter* currentNode) { 1019 assert(current != nullptr, "invariant"); 1020 assert(current->thread_state() != _thread_blocked, "invariant"); 1021 assert(currentNode != nullptr, "invariant"); 1022 assert(currentNode->_thread == current, "invariant"); 1023 assert(_waiters > 0, "invariant"); 1024 assert_mark_word_consistency(); 1025 1026 for (;;) { 1027 ObjectWaiter::TStates v = currentNode->TState; 1028 guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant"); 1029 assert(owner_raw() != current, "invariant"); 1030 1031 // This thread has been notified so try to reacquire the lock. 1032 if (TryLock(current) == TryLockResult::Success) { 1033 break; 1034 } 1035 1036 // If that fails, spin again. Note that spin count may be zero so the above TryLock 1037 // is necessary. 1038 if (TrySpin(current)) { 1039 break; 1040 } 1041 1042 { 1043 OSThreadContendState osts(current->osthread()); 1044 1045 assert(current->thread_state() == _thread_in_vm, "invariant"); 1046 1047 { 1048 ClearSuccOnSuspend csos(this); 1049 ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */); 1050 current->_ParkEvent->park(); 1051 } 1052 } 1053 1054 // Try again, but just so we distinguish between futile wakeups and 1055 // successful wakeups. The following test isn't algorithmically 1056 // necessary, but it helps us maintain sensible statistics. 1057 if (TryLock(current) == TryLockResult::Success) { 1058 break; 1059 } 1060 1061 // The lock is still contested. 1062 1063 // Assuming this is not a spurious wakeup we'll normally 1064 // find that _succ == current. 1065 if (_succ == current) _succ = nullptr; 1066 1067 // Invariant: after clearing _succ a contending thread 1068 // *must* retry _owner before parking. 1069 OrderAccess::fence(); 1070 1071 // Keep a tally of the # of futile wakeups. 1072 // Note that the counter is not protected by a lock or updated by atomics. 1073 // That is by design - we trade "lossy" counters which are exposed to 1074 // races during updates for a lower probe effect. 1075 // This PerfData object can be used in parallel with a safepoint. 1076 // See the work around in PerfDataManager::destroy(). 1077 OM_PERFDATA_OP(FutileWakeups, inc()); 1078 } 1079 1080 // current has acquired the lock -- Unlink current from the cxq or EntryList . 1081 // Normally we'll find current on the EntryList. 1082 // Unlinking from the EntryList is constant-time and atomic-free. 1083 // From the perspective of the lock owner (this thread), the 1084 // EntryList is stable and cxq is prepend-only. 1085 // The head of cxq is volatile but the interior is stable. 1086 // In addition, current.TState is stable. 1087 1088 assert(owner_raw() == current, "invariant"); 1089 assert_mark_word_consistency(); 1090 UnlinkAfterAcquire(current, currentNode); 1091 if (_succ == current) _succ = nullptr; 1092 assert(_succ != current, "invariant"); 1093 currentNode->TState = ObjectWaiter::TS_RUN; 1094 OrderAccess::fence(); // see comments at the end of EnterI() 1095 } 1096 1097 // By convention we unlink a contending thread from EntryList|cxq immediately 1098 // after the thread acquires the lock in ::enter(). Equally, we could defer 1099 // unlinking the thread until ::exit()-time. 1100 1101 void ObjectMonitor::UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* currentNode) { 1102 assert(owner_raw() == current, "invariant"); 1103 assert(currentNode->_thread == current, "invariant"); 1104 1105 if (currentNode->TState == ObjectWaiter::TS_ENTER) { 1106 // Normal case: remove current from the DLL EntryList . 1107 // This is a constant-time operation. 1108 ObjectWaiter* nxt = currentNode->_next; 1109 ObjectWaiter* prv = currentNode->_prev; 1110 if (nxt != nullptr) nxt->_prev = prv; 1111 if (prv != nullptr) prv->_next = nxt; 1112 if (currentNode == _EntryList) _EntryList = nxt; 1113 assert(nxt == nullptr || nxt->TState == ObjectWaiter::TS_ENTER, "invariant"); 1114 assert(prv == nullptr || prv->TState == ObjectWaiter::TS_ENTER, "invariant"); 1115 } else { 1116 assert(currentNode->TState == ObjectWaiter::TS_CXQ, "invariant"); 1117 // Inopportune interleaving -- current is still on the cxq. 1118 // This usually means the enqueue of self raced an exiting thread. 1119 // Normally we'll find current near the front of the cxq, so 1120 // dequeueing is typically fast. If needbe we can accelerate 1121 // this with some MCS/CHL-like bidirectional list hints and advisory 1122 // back-links so dequeueing from the interior will normally operate 1123 // in constant-time. 1124 // Dequeue current from either the head (with CAS) or from the interior 1125 // with a linear-time scan and normal non-atomic memory operations. 1126 // CONSIDER: if current is on the cxq then simply drain cxq into EntryList 1127 // and then unlink current from EntryList. We have to drain eventually, 1128 // so it might as well be now. 1129 1130 ObjectWaiter* v = _cxq; 1131 assert(v != nullptr, "invariant"); 1132 if (v != currentNode || Atomic::cmpxchg(&_cxq, v, currentNode->_next) != v) { 1133 // The CAS above can fail from interference IFF a "RAT" arrived. 1134 // In that case current must be in the interior and can no longer be 1135 // at the head of cxq. 1136 if (v == currentNode) { 1137 assert(_cxq != v, "invariant"); 1138 v = _cxq; // CAS above failed - start scan at head of list 1139 } 1140 ObjectWaiter* p; 1141 ObjectWaiter* q = nullptr; 1142 for (p = v; p != nullptr && p != currentNode; p = p->_next) { 1143 q = p; 1144 assert(p->TState == ObjectWaiter::TS_CXQ, "invariant"); 1145 } 1146 assert(v != currentNode, "invariant"); 1147 assert(p == currentNode, "Node not found on cxq"); 1148 assert(p != _cxq, "invariant"); 1149 assert(q != nullptr, "invariant"); 1150 assert(q->_next == p, "invariant"); 1151 q->_next = p->_next; 1152 } 1153 } 1154 1155 #ifdef ASSERT 1156 // Diagnostic hygiene ... 1157 currentNode->_prev = (ObjectWaiter*) 0xBAD; 1158 currentNode->_next = (ObjectWaiter*) 0xBAD; 1159 currentNode->TState = ObjectWaiter::TS_RUN; 1160 #endif 1161 } 1162 1163 // ----------------------------------------------------------------------------- 1164 // Exit support 1165 // 1166 // exit() 1167 // ~~~~~~ 1168 // Note that the collector can't reclaim the objectMonitor or deflate 1169 // the object out from underneath the thread calling ::exit() as the 1170 // thread calling ::exit() never transitions to a stable state. 1171 // This inhibits GC, which in turn inhibits asynchronous (and 1172 // inopportune) reclamation of "this". 1173 // 1174 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ; 1175 // There's one exception to the claim above, however. EnterI() can call 1176 // exit() to drop a lock if the acquirer has been externally suspended. 1177 // In that case exit() is called with _thread_state == _thread_blocked, 1178 // but the monitor's _contentions field is > 0, which inhibits reclamation. 1179 // 1180 // 1-0 exit 1181 // ~~~~~~~~ 1182 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of 1183 // the fast-path operators have been optimized so the common ::exit() 1184 // operation is 1-0, e.g., see macroAssembler_x86.cpp: fast_unlock(). 1185 // The code emitted by fast_unlock() elides the usual MEMBAR. This 1186 // greatly improves latency -- MEMBAR and CAS having considerable local 1187 // latency on modern processors -- but at the cost of "stranding". Absent the 1188 // MEMBAR, a thread in fast_unlock() can race a thread in the slow 1189 // ::enter() path, resulting in the entering thread being stranding 1190 // and a progress-liveness failure. Stranding is extremely rare. 1191 // We use timers (timed park operations) & periodic polling to detect 1192 // and recover from stranding. Potentially stranded threads periodically 1193 // wake up and poll the lock. See the usage of the _Responsible variable. 1194 // 1195 // The CAS() in enter provides for safety and exclusion, while the CAS or 1196 // MEMBAR in exit provides for progress and avoids stranding. 1-0 locking 1197 // eliminates the CAS/MEMBAR from the exit path, but it admits stranding. 1198 // We detect and recover from stranding with timers. 1199 // 1200 // If a thread transiently strands it'll park until (a) another 1201 // thread acquires the lock and then drops the lock, at which time the 1202 // exiting thread will notice and unpark the stranded thread, or, (b) 1203 // the timer expires. If the lock is high traffic then the stranding latency 1204 // will be low due to (a). If the lock is low traffic then the odds of 1205 // stranding are lower, although the worst-case stranding latency 1206 // is longer. Critically, we don't want to put excessive load in the 1207 // platform's timer subsystem. We want to minimize both the timer injection 1208 // rate (timers created/sec) as well as the number of timers active at 1209 // any one time. (more precisely, we want to minimize timer-seconds, which is 1210 // the integral of the # of active timers at any instant over time). 1211 // Both impinge on OS scalability. Given that, at most one thread parked on 1212 // a monitor will use a timer. 1213 // 1214 // There is also the risk of a futile wake-up. If we drop the lock 1215 // another thread can reacquire the lock immediately, and we can 1216 // then wake a thread unnecessarily. This is benign, and we've 1217 // structured the code so the windows are short and the frequency 1218 // of such futile wakups is low. 1219 1220 void ObjectMonitor::exit(JavaThread* current, bool not_suspended) { 1221 void* cur = owner_raw(); 1222 if (current != cur) { 1223 if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) { 1224 assert(_recursions == 0, "invariant"); 1225 set_owner_from_BasicLock(cur, current); // Convert from BasicLock* to Thread*. 1226 _recursions = 0; 1227 } else { 1228 // Apparent unbalanced locking ... 1229 // Naively we'd like to throw IllegalMonitorStateException. 1230 // As a practical matter we can neither allocate nor throw an 1231 // exception as ::exit() can be called from leaf routines. 1232 // see x86_32.ad Fast_Unlock() and the I1 and I2 properties. 1233 // Upon deeper reflection, however, in a properly run JVM the only 1234 // way we should encounter this situation is in the presence of 1235 // unbalanced JNI locking. TODO: CheckJNICalls. 1236 // See also: CR4414101 1237 #ifdef ASSERT 1238 LogStreamHandle(Error, monitorinflation) lsh; 1239 lsh.print_cr("ERROR: ObjectMonitor::exit(): thread=" INTPTR_FORMAT 1240 " is exiting an ObjectMonitor it does not own.", p2i(current)); 1241 lsh.print_cr("The imbalance is possibly caused by JNI locking."); 1242 print_debug_style_on(&lsh); 1243 assert(false, "Non-balanced monitor enter/exit!"); 1244 #endif 1245 return; 1246 } 1247 } 1248 1249 if (_recursions != 0) { 1250 _recursions--; // this is simple recursive enter 1251 return; 1252 } 1253 1254 // Invariant: after setting Responsible=null an thread must execute 1255 // a MEMBAR or other serializing instruction before fetching EntryList|cxq. 1256 _Responsible = nullptr; 1257 1258 #if INCLUDE_JFR 1259 // get the owner's thread id for the MonitorEnter event 1260 // if it is enabled and the thread isn't suspended 1261 if (not_suspended && EventJavaMonitorEnter::is_enabled()) { 1262 _previous_owner_tid = JFR_THREAD_ID(current); 1263 } 1264 #endif 1265 1266 for (;;) { 1267 assert(current == owner_raw(), "invariant"); 1268 1269 // Drop the lock. 1270 // release semantics: prior loads and stores from within the critical section 1271 // must not float (reorder) past the following store that drops the lock. 1272 // Uses a storeload to separate release_store(owner) from the 1273 // successor check. The try_set_owner() below uses cmpxchg() so 1274 // we get the fence down there. 1275 release_clear_owner(current); 1276 OrderAccess::storeload(); 1277 1278 if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != nullptr) { 1279 return; 1280 } 1281 // Other threads are blocked trying to acquire the lock. 1282 1283 // Normally the exiting thread is responsible for ensuring succession, 1284 // but if other successors are ready or other entering threads are spinning 1285 // then this thread can simply store null into _owner and exit without 1286 // waking a successor. The existence of spinners or ready successors 1287 // guarantees proper succession (liveness). Responsibility passes to the 1288 // ready or running successors. The exiting thread delegates the duty. 1289 // More precisely, if a successor already exists this thread is absolved 1290 // of the responsibility of waking (unparking) one. 1291 // 1292 // The _succ variable is critical to reducing futile wakeup frequency. 1293 // _succ identifies the "heir presumptive" thread that has been made 1294 // ready (unparked) but that has not yet run. We need only one such 1295 // successor thread to guarantee progress. 1296 // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf 1297 // section 3.3 "Futile Wakeup Throttling" for details. 1298 // 1299 // Note that spinners in Enter() also set _succ non-null. 1300 // In the current implementation spinners opportunistically set 1301 // _succ so that exiting threads might avoid waking a successor. 1302 // Another less appealing alternative would be for the exiting thread 1303 // to drop the lock and then spin briefly to see if a spinner managed 1304 // to acquire the lock. If so, the exiting thread could exit 1305 // immediately without waking a successor, otherwise the exiting 1306 // thread would need to dequeue and wake a successor. 1307 // (Note that we'd need to make the post-drop spin short, but no 1308 // shorter than the worst-case round-trip cache-line migration time. 1309 // The dropped lock needs to become visible to the spinner, and then 1310 // the acquisition of the lock by the spinner must become visible to 1311 // the exiting thread). 1312 1313 // It appears that an heir-presumptive (successor) must be made ready. 1314 // Only the current lock owner can manipulate the EntryList or 1315 // drain _cxq, so we need to reacquire the lock. If we fail 1316 // to reacquire the lock the responsibility for ensuring succession 1317 // falls to the new owner. 1318 // 1319 if (try_set_owner_from(nullptr, current) != nullptr) { 1320 return; 1321 } 1322 1323 guarantee(owner_raw() == current, "invariant"); 1324 1325 ObjectWaiter* w = nullptr; 1326 1327 w = _EntryList; 1328 if (w != nullptr) { 1329 // I'd like to write: guarantee (w->_thread != current). 1330 // But in practice an exiting thread may find itself on the EntryList. 1331 // Let's say thread T1 calls O.wait(). Wait() enqueues T1 on O's waitset and 1332 // then calls exit(). Exit release the lock by setting O._owner to null. 1333 // Let's say T1 then stalls. T2 acquires O and calls O.notify(). The 1334 // notify() operation moves T1 from O's waitset to O's EntryList. T2 then 1335 // release the lock "O". T2 resumes immediately after the ST of null into 1336 // _owner, above. T2 notices that the EntryList is populated, so it 1337 // reacquires the lock and then finds itself on the EntryList. 1338 // Given all that, we have to tolerate the circumstance where "w" is 1339 // associated with current. 1340 assert(w->TState == ObjectWaiter::TS_ENTER, "invariant"); 1341 ExitEpilog(current, w); 1342 return; 1343 } 1344 1345 // If we find that both _cxq and EntryList are null then just 1346 // re-run the exit protocol from the top. 1347 w = _cxq; 1348 if (w == nullptr) continue; 1349 1350 // Drain _cxq into EntryList - bulk transfer. 1351 // First, detach _cxq. 1352 // The following loop is tantamount to: w = swap(&cxq, nullptr) 1353 for (;;) { 1354 assert(w != nullptr, "Invariant"); 1355 ObjectWaiter* u = Atomic::cmpxchg(&_cxq, w, (ObjectWaiter*)nullptr); 1356 if (u == w) break; 1357 w = u; 1358 } 1359 1360 assert(w != nullptr, "invariant"); 1361 assert(_EntryList == nullptr, "invariant"); 1362 1363 // Convert the LIFO SLL anchored by _cxq into a DLL. 1364 // The list reorganization step operates in O(LENGTH(w)) time. 1365 // It's critical that this step operate quickly as 1366 // "current" still holds the outer-lock, restricting parallelism 1367 // and effectively lengthening the critical section. 1368 // Invariant: s chases t chases u. 1369 // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so 1370 // we have faster access to the tail. 1371 1372 _EntryList = w; 1373 ObjectWaiter* q = nullptr; 1374 ObjectWaiter* p; 1375 for (p = w; p != nullptr; p = p->_next) { 1376 guarantee(p->TState == ObjectWaiter::TS_CXQ, "Invariant"); 1377 p->TState = ObjectWaiter::TS_ENTER; 1378 p->_prev = q; 1379 q = p; 1380 } 1381 1382 // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = nullptr 1383 // The MEMBAR is satisfied by the release_store() operation in ExitEpilog(). 1384 1385 // See if we can abdicate to a spinner instead of waking a thread. 1386 // A primary goal of the implementation is to reduce the 1387 // context-switch rate. 1388 if (_succ != nullptr) continue; 1389 1390 w = _EntryList; 1391 if (w != nullptr) { 1392 guarantee(w->TState == ObjectWaiter::TS_ENTER, "invariant"); 1393 ExitEpilog(current, w); 1394 return; 1395 } 1396 } 1397 } 1398 1399 void ObjectMonitor::ExitEpilog(JavaThread* current, ObjectWaiter* Wakee) { 1400 assert(owner_raw() == current, "invariant"); 1401 1402 // Exit protocol: 1403 // 1. ST _succ = wakee 1404 // 2. membar #loadstore|#storestore; 1405 // 2. ST _owner = nullptr 1406 // 3. unpark(wakee) 1407 1408 _succ = Wakee->_thread; 1409 ParkEvent * Trigger = Wakee->_event; 1410 1411 // Hygiene -- once we've set _owner = nullptr we can't safely dereference Wakee again. 1412 // The thread associated with Wakee may have grabbed the lock and "Wakee" may be 1413 // out-of-scope (non-extant). 1414 Wakee = nullptr; 1415 1416 // Drop the lock. 1417 // Uses a fence to separate release_store(owner) from the LD in unpark(). 1418 release_clear_owner(current); 1419 OrderAccess::fence(); 1420 1421 DTRACE_MONITOR_PROBE(contended__exit, this, object(), current); 1422 Trigger->unpark(); 1423 1424 // Maintain stats and report events to JVMTI 1425 OM_PERFDATA_OP(Parks, inc()); 1426 } 1427 1428 // complete_exit exits a lock returning recursion count 1429 // complete_exit requires an inflated monitor 1430 // The _owner field is not always the Thread addr even with an 1431 // inflated monitor, e.g. the monitor can be inflated by a non-owning 1432 // thread due to contention. 1433 intx ObjectMonitor::complete_exit(JavaThread* current) { 1434 assert(InitDone, "Unexpectedly not initialized"); 1435 1436 void* cur = owner_raw(); 1437 if (current != cur) { 1438 if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) { 1439 assert(_recursions == 0, "internal state error"); 1440 set_owner_from_BasicLock(cur, current); // Convert from BasicLock* to Thread*. 1441 _recursions = 0; 1442 } 1443 } 1444 1445 guarantee(current == owner_raw(), "complete_exit not owner"); 1446 intx save = _recursions; // record the old recursion count 1447 _recursions = 0; // set the recursion level to be 0 1448 exit(current); // exit the monitor 1449 guarantee(owner_raw() != current, "invariant"); 1450 return save; 1451 } 1452 1453 // Checks that the current THREAD owns this monitor and causes an 1454 // immediate return if it doesn't. We don't use the CHECK macro 1455 // because we want the IMSE to be the only exception that is thrown 1456 // from the call site when false is returned. Any other pending 1457 // exception is ignored. 1458 #define CHECK_OWNER() \ 1459 do { \ 1460 if (!check_owner(THREAD)) { \ 1461 assert(HAS_PENDING_EXCEPTION, "expected a pending IMSE here."); \ 1462 return; \ 1463 } \ 1464 } while (false) 1465 1466 // Returns true if the specified thread owns the ObjectMonitor. 1467 // Otherwise returns false and throws IllegalMonitorStateException 1468 // (IMSE). If there is a pending exception and the specified thread 1469 // is not the owner, that exception will be replaced by the IMSE. 1470 bool ObjectMonitor::check_owner(TRAPS) { 1471 JavaThread* current = THREAD; 1472 void* cur = owner_raw(); 1473 assert(cur != anon_owner_ptr(), "no anon owner here"); 1474 if (cur == current) { 1475 return true; 1476 } 1477 if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) { 1478 set_owner_from_BasicLock(cur, current); // Convert from BasicLock* to Thread*. 1479 _recursions = 0; 1480 return true; 1481 } 1482 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(), 1483 "current thread is not owner", false); 1484 } 1485 1486 static inline bool is_excluded(const Klass* monitor_klass) { 1487 assert(monitor_klass != nullptr, "invariant"); 1488 NOT_JFR_RETURN_(false); 1489 JFR_ONLY(return vmSymbols::jdk_jfr_internal_HiddenWait() == monitor_klass->name();) 1490 } 1491 1492 static void post_monitor_wait_event(EventJavaMonitorWait* event, 1493 ObjectMonitor* monitor, 1494 uint64_t notifier_tid, 1495 jlong timeout, 1496 bool timedout) { 1497 assert(event != nullptr, "invariant"); 1498 assert(monitor != nullptr, "invariant"); 1499 const Klass* monitor_klass = monitor->object()->klass(); 1500 if (is_excluded(monitor_klass)) { 1501 return; 1502 } 1503 event->set_monitorClass(monitor_klass); 1504 event->set_timeout(timeout); 1505 // Set an address that is 'unique enough', such that events close in 1506 // time and with the same address are likely (but not guaranteed) to 1507 // belong to the same object. 1508 event->set_address((uintptr_t)monitor); 1509 event->set_notifier(notifier_tid); 1510 event->set_timedOut(timedout); 1511 event->commit(); 1512 } 1513 1514 // ----------------------------------------------------------------------------- 1515 // Wait/Notify/NotifyAll 1516 // 1517 // Note: a subset of changes to ObjectMonitor::wait() 1518 // will need to be replicated in complete_exit 1519 void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) { 1520 JavaThread* current = THREAD; 1521 1522 assert(InitDone, "Unexpectedly not initialized"); 1523 1524 CHECK_OWNER(); // Throws IMSE if not owner. 1525 1526 EventJavaMonitorWait event; 1527 1528 // check for a pending interrupt 1529 if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) { 1530 // post monitor waited event. Note that this is past-tense, we are done waiting. 1531 if (JvmtiExport::should_post_monitor_waited()) { 1532 // Note: 'false' parameter is passed here because the 1533 // wait was not timed out due to thread interrupt. 1534 JvmtiExport::post_monitor_waited(current, this, false); 1535 1536 // In this short circuit of the monitor wait protocol, the 1537 // current thread never drops ownership of the monitor and 1538 // never gets added to the wait queue so the current thread 1539 // cannot be made the successor. This means that the 1540 // JVMTI_EVENT_MONITOR_WAITED event handler cannot accidentally 1541 // consume an unpark() meant for the ParkEvent associated with 1542 // this ObjectMonitor. 1543 } 1544 if (event.should_commit()) { 1545 post_monitor_wait_event(&event, this, 0, millis, false); 1546 } 1547 THROW(vmSymbols::java_lang_InterruptedException()); 1548 return; 1549 } 1550 1551 current->set_current_waiting_monitor(this); 1552 1553 // create a node to be put into the queue 1554 // Critically, after we reset() the event but prior to park(), we must check 1555 // for a pending interrupt. 1556 ObjectWaiter node(current); 1557 node.TState = ObjectWaiter::TS_WAIT; 1558 current->_ParkEvent->reset(); 1559 OrderAccess::fence(); // ST into Event; membar ; LD interrupted-flag 1560 1561 // Enter the waiting queue, which is a circular doubly linked list in this case 1562 // but it could be a priority queue or any data structure. 1563 // _WaitSetLock protects the wait queue. Normally the wait queue is accessed only 1564 // by the owner of the monitor *except* in the case where park() 1565 // returns because of a timeout of interrupt. Contention is exceptionally rare 1566 // so we use a simple spin-lock instead of a heavier-weight blocking lock. 1567 1568 Thread::SpinAcquire(&_WaitSetLock, "WaitSet - add"); 1569 AddWaiter(&node); 1570 Thread::SpinRelease(&_WaitSetLock); 1571 1572 _Responsible = nullptr; 1573 1574 intx save = _recursions; // record the old recursion count 1575 _waiters++; // increment the number of waiters 1576 _recursions = 0; // set the recursion level to be 1 1577 exit(current); // exit the monitor 1578 guarantee(owner_raw() != current, "invariant"); 1579 1580 // The thread is on the WaitSet list - now park() it. 1581 // On MP systems it's conceivable that a brief spin before we park 1582 // could be profitable. 1583 // 1584 // TODO-FIXME: change the following logic to a loop of the form 1585 // while (!timeout && !interrupted && _notified == 0) park() 1586 1587 int ret = OS_OK; 1588 int WasNotified = 0; 1589 1590 // Need to check interrupt state whilst still _thread_in_vm 1591 bool interrupted = interruptible && current->is_interrupted(false); 1592 1593 { // State transition wrappers 1594 OSThread* osthread = current->osthread(); 1595 OSThreadWaitState osts(osthread, true); 1596 1597 assert(current->thread_state() == _thread_in_vm, "invariant"); 1598 1599 { 1600 ClearSuccOnSuspend csos(this); 1601 ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */); 1602 if (interrupted || HAS_PENDING_EXCEPTION) { 1603 // Intentionally empty 1604 } else if (node._notified == 0) { 1605 if (millis <= 0) { 1606 current->_ParkEvent->park(); 1607 } else { 1608 ret = current->_ParkEvent->park(millis); 1609 } 1610 } 1611 } 1612 1613 // Node may be on the WaitSet, the EntryList (or cxq), or in transition 1614 // from the WaitSet to the EntryList. 1615 // See if we need to remove Node from the WaitSet. 1616 // We use double-checked locking to avoid grabbing _WaitSetLock 1617 // if the thread is not on the wait queue. 1618 // 1619 // Note that we don't need a fence before the fetch of TState. 1620 // In the worst case we'll fetch a old-stale value of TS_WAIT previously 1621 // written by the is thread. (perhaps the fetch might even be satisfied 1622 // by a look-aside into the processor's own store buffer, although given 1623 // the length of the code path between the prior ST and this load that's 1624 // highly unlikely). If the following LD fetches a stale TS_WAIT value 1625 // then we'll acquire the lock and then re-fetch a fresh TState value. 1626 // That is, we fail toward safety. 1627 1628 if (node.TState == ObjectWaiter::TS_WAIT) { 1629 Thread::SpinAcquire(&_WaitSetLock, "WaitSet - unlink"); 1630 if (node.TState == ObjectWaiter::TS_WAIT) { 1631 DequeueSpecificWaiter(&node); // unlink from WaitSet 1632 assert(node._notified == 0, "invariant"); 1633 node.TState = ObjectWaiter::TS_RUN; 1634 } 1635 Thread::SpinRelease(&_WaitSetLock); 1636 } 1637 1638 // The thread is now either on off-list (TS_RUN), 1639 // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ). 1640 // The Node's TState variable is stable from the perspective of this thread. 1641 // No other threads will asynchronously modify TState. 1642 guarantee(node.TState != ObjectWaiter::TS_WAIT, "invariant"); 1643 OrderAccess::loadload(); 1644 if (_succ == current) _succ = nullptr; 1645 WasNotified = node._notified; 1646 1647 // Reentry phase -- reacquire the monitor. 1648 // re-enter contended monitor after object.wait(). 1649 // retain OBJECT_WAIT state until re-enter successfully completes 1650 // Thread state is thread_in_vm and oop access is again safe, 1651 // although the raw address of the object may have changed. 1652 // (Don't cache naked oops over safepoints, of course). 1653 1654 // post monitor waited event. Note that this is past-tense, we are done waiting. 1655 if (JvmtiExport::should_post_monitor_waited()) { 1656 JvmtiExport::post_monitor_waited(current, this, ret == OS_TIMEOUT); 1657 1658 if (node._notified != 0 && _succ == current) { 1659 // In this part of the monitor wait-notify-reenter protocol it 1660 // is possible (and normal) for another thread to do a fastpath 1661 // monitor enter-exit while this thread is still trying to get 1662 // to the reenter portion of the protocol. 1663 // 1664 // The ObjectMonitor was notified and the current thread is 1665 // the successor which also means that an unpark() has already 1666 // been done. The JVMTI_EVENT_MONITOR_WAITED event handler can 1667 // consume the unpark() that was done when the successor was 1668 // set because the same ParkEvent is shared between Java 1669 // monitors and JVM/TI RawMonitors (for now). 1670 // 1671 // We redo the unpark() to ensure forward progress, i.e., we 1672 // don't want all pending threads hanging (parked) with none 1673 // entering the unlocked monitor. 1674 node._event->unpark(); 1675 } 1676 } 1677 1678 if (event.should_commit()) { 1679 post_monitor_wait_event(&event, this, node._notifier_tid, millis, ret == OS_TIMEOUT); 1680 } 1681 1682 OrderAccess::fence(); 1683 1684 assert(owner_raw() != current, "invariant"); 1685 ObjectWaiter::TStates v = node.TState; 1686 if (v == ObjectWaiter::TS_RUN) { 1687 enter(current); 1688 } else { 1689 guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant"); 1690 ReenterI(current, &node); 1691 node.wait_reenter_end(this); 1692 } 1693 1694 // current has reacquired the lock. 1695 // Lifecycle - the node representing current must not appear on any queues. 1696 // Node is about to go out-of-scope, but even if it were immortal we wouldn't 1697 // want residual elements associated with this thread left on any lists. 1698 guarantee(node.TState == ObjectWaiter::TS_RUN, "invariant"); 1699 assert(owner_raw() == current, "invariant"); 1700 assert(_succ != current, "invariant"); 1701 } // OSThreadWaitState() 1702 1703 current->set_current_waiting_monitor(nullptr); 1704 1705 guarantee(_recursions == 0, "invariant"); 1706 int relock_count = JvmtiDeferredUpdates::get_and_reset_relock_count_after_wait(current); 1707 _recursions = save // restore the old recursion count 1708 + relock_count; // increased by the deferred relock count 1709 current->inc_held_monitor_count(relock_count); // Deopt never entered these counts. 1710 _waiters--; // decrement the number of waiters 1711 1712 // Verify a few postconditions 1713 assert(owner_raw() == current, "invariant"); 1714 assert(_succ != current, "invariant"); 1715 assert_mark_word_consistency(); 1716 1717 // check if the notification happened 1718 if (!WasNotified) { 1719 // no, it could be timeout or Thread.interrupt() or both 1720 // check for interrupt event, otherwise it is timeout 1721 if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) { 1722 THROW(vmSymbols::java_lang_InterruptedException()); 1723 } 1724 } 1725 1726 // NOTE: Spurious wake up will be consider as timeout. 1727 // Monitor notify has precedence over thread interrupt. 1728 } 1729 1730 1731 // Consider: 1732 // If the lock is cool (cxq == null && succ == null) and we're on an MP system 1733 // then instead of transferring a thread from the WaitSet to the EntryList 1734 // we might just dequeue a thread from the WaitSet and directly unpark() it. 1735 1736 void ObjectMonitor::INotify(JavaThread* current) { 1737 Thread::SpinAcquire(&_WaitSetLock, "WaitSet - notify"); 1738 ObjectWaiter* iterator = DequeueWaiter(); 1739 if (iterator != nullptr) { 1740 guarantee(iterator->TState == ObjectWaiter::TS_WAIT, "invariant"); 1741 guarantee(iterator->_notified == 0, "invariant"); 1742 // Disposition - what might we do with iterator ? 1743 // a. add it directly to the EntryList - either tail (policy == 1) 1744 // or head (policy == 0). 1745 // b. push it onto the front of the _cxq (policy == 2). 1746 // For now we use (b). 1747 1748 iterator->TState = ObjectWaiter::TS_ENTER; 1749 1750 iterator->_notified = 1; 1751 iterator->_notifier_tid = JFR_THREAD_ID(current); 1752 1753 ObjectWaiter* list = _EntryList; 1754 if (list != nullptr) { 1755 assert(list->_prev == nullptr, "invariant"); 1756 assert(list->TState == ObjectWaiter::TS_ENTER, "invariant"); 1757 assert(list != iterator, "invariant"); 1758 } 1759 1760 // prepend to cxq 1761 if (list == nullptr) { 1762 iterator->_next = iterator->_prev = nullptr; 1763 _EntryList = iterator; 1764 } else { 1765 iterator->TState = ObjectWaiter::TS_CXQ; 1766 for (;;) { 1767 ObjectWaiter* front = _cxq; 1768 iterator->_next = front; 1769 if (Atomic::cmpxchg(&_cxq, front, iterator) == front) { 1770 break; 1771 } 1772 } 1773 } 1774 1775 // _WaitSetLock protects the wait queue, not the EntryList. We could 1776 // move the add-to-EntryList operation, above, outside the critical section 1777 // protected by _WaitSetLock. In practice that's not useful. With the 1778 // exception of wait() timeouts and interrupts the monitor owner 1779 // is the only thread that grabs _WaitSetLock. There's almost no contention 1780 // on _WaitSetLock so it's not profitable to reduce the length of the 1781 // critical section. 1782 1783 iterator->wait_reenter_begin(this); 1784 } 1785 Thread::SpinRelease(&_WaitSetLock); 1786 } 1787 1788 // Consider: a not-uncommon synchronization bug is to use notify() when 1789 // notifyAll() is more appropriate, potentially resulting in stranded 1790 // threads; this is one example of a lost wakeup. A useful diagnostic 1791 // option is to force all notify() operations to behave as notifyAll(). 1792 // 1793 // Note: We can also detect many such problems with a "minimum wait". 1794 // When the "minimum wait" is set to a small non-zero timeout value 1795 // and the program does not hang whereas it did absent "minimum wait", 1796 // that suggests a lost wakeup bug. 1797 1798 void ObjectMonitor::notify(TRAPS) { 1799 JavaThread* current = THREAD; 1800 CHECK_OWNER(); // Throws IMSE if not owner. 1801 if (_WaitSet == nullptr) { 1802 return; 1803 } 1804 DTRACE_MONITOR_PROBE(notify, this, object(), current); 1805 INotify(current); 1806 OM_PERFDATA_OP(Notifications, inc(1)); 1807 } 1808 1809 1810 // The current implementation of notifyAll() transfers the waiters one-at-a-time 1811 // from the waitset to the EntryList. This could be done more efficiently with a 1812 // single bulk transfer but in practice it's not time-critical. Beware too, 1813 // that in prepend-mode we invert the order of the waiters. Let's say that the 1814 // waitset is "ABCD" and the EntryList is "XYZ". After a notifyAll() in prepend 1815 // mode the waitset will be empty and the EntryList will be "DCBAXYZ". 1816 1817 void ObjectMonitor::notifyAll(TRAPS) { 1818 JavaThread* current = THREAD; 1819 CHECK_OWNER(); // Throws IMSE if not owner. 1820 if (_WaitSet == nullptr) { 1821 return; 1822 } 1823 1824 DTRACE_MONITOR_PROBE(notifyAll, this, object(), current); 1825 int tally = 0; 1826 while (_WaitSet != nullptr) { 1827 tally++; 1828 INotify(current); 1829 } 1830 1831 OM_PERFDATA_OP(Notifications, inc(tally)); 1832 } 1833 1834 // ----------------------------------------------------------------------------- 1835 // Adaptive Spinning Support 1836 // 1837 // Adaptive spin-then-block - rational spinning 1838 // 1839 // Note that we spin "globally" on _owner with a classic SMP-polite TATAS 1840 // algorithm. On high order SMP systems it would be better to start with 1841 // a brief global spin and then revert to spinning locally. In the spirit of MCS/CLH, 1842 // a contending thread could enqueue itself on the cxq and then spin locally 1843 // on a thread-specific variable such as its ParkEvent._Event flag. 1844 // That's left as an exercise for the reader. Note that global spinning is 1845 // not problematic on Niagara, as the L2 cache serves the interconnect and 1846 // has both low latency and massive bandwidth. 1847 // 1848 // Broadly, we can fix the spin frequency -- that is, the % of contended lock 1849 // acquisition attempts where we opt to spin -- at 100% and vary the spin count 1850 // (duration) or we can fix the count at approximately the duration of 1851 // a context switch and vary the frequency. Of course we could also 1852 // vary both satisfying K == Frequency * Duration, where K is adaptive by monitor. 1853 // For a description of 'Adaptive spin-then-block mutual exclusion in 1854 // multi-threaded processing,' see U.S. Pat. No. 8046758. 1855 // 1856 // This implementation varies the duration "D", where D varies with 1857 // the success rate of recent spin attempts. (D is capped at approximately 1858 // length of a round-trip context switch). The success rate for recent 1859 // spin attempts is a good predictor of the success rate of future spin 1860 // attempts. The mechanism adapts automatically to varying critical 1861 // section length (lock modality), system load and degree of parallelism. 1862 // D is maintained per-monitor in _SpinDuration and is initialized 1863 // optimistically. Spin frequency is fixed at 100%. 1864 // 1865 // Note that _SpinDuration is volatile, but we update it without locks 1866 // or atomics. The code is designed so that _SpinDuration stays within 1867 // a reasonable range even in the presence of races. The arithmetic 1868 // operations on _SpinDuration are closed over the domain of legal values, 1869 // so at worst a race will install and older but still legal value. 1870 // At the very worst this introduces some apparent non-determinism. 1871 // We might spin when we shouldn't or vice-versa, but since the spin 1872 // count are relatively short, even in the worst case, the effect is harmless. 1873 // 1874 // Care must be taken that a low "D" value does not become an 1875 // an absorbing state. Transient spinning failures -- when spinning 1876 // is overall profitable -- should not cause the system to converge 1877 // on low "D" values. We want spinning to be stable and predictable 1878 // and fairly responsive to change and at the same time we don't want 1879 // it to oscillate, become metastable, be "too" non-deterministic, 1880 // or converge on or enter undesirable stable absorbing states. 1881 // 1882 // We implement a feedback-based control system -- using past behavior 1883 // to predict future behavior. We face two issues: (a) if the 1884 // input signal is random then the spin predictor won't provide optimal 1885 // results, and (b) if the signal frequency is too high then the control 1886 // system, which has some natural response lag, will "chase" the signal. 1887 // (b) can arise from multimodal lock hold times. Transient preemption 1888 // can also result in apparent bimodal lock hold times. 1889 // Although sub-optimal, neither condition is particularly harmful, as 1890 // in the worst-case we'll spin when we shouldn't or vice-versa. 1891 // The maximum spin duration is rather short so the failure modes aren't bad. 1892 // To be conservative, I've tuned the gain in system to bias toward 1893 // _not spinning. Relatedly, the system can sometimes enter a mode where it 1894 // "rings" or oscillates between spinning and not spinning. This happens 1895 // when spinning is just on the cusp of profitability, however, so the 1896 // situation is not dire. The state is benign -- there's no need to add 1897 // hysteresis control to damp the transition rate between spinning and 1898 // not spinning. 1899 1900 int ObjectMonitor::Knob_SpinLimit = 5000; // derived by an external tool 1901 1902 static int Knob_Bonus = 100; // spin success bonus 1903 static int Knob_Penalty = 200; // spin failure penalty 1904 static int Knob_Poverty = 1000; 1905 static int Knob_FixedSpin = 0; 1906 static int Knob_PreSpin = 10; // 20-100 likely better, but it's not better in my testing. 1907 1908 inline static int adjust_up(int spin_duration) { 1909 int x = spin_duration; 1910 if (x < ObjectMonitor::Knob_SpinLimit) { 1911 if (x < Knob_Poverty) { 1912 x = Knob_Poverty; 1913 } 1914 return x + Knob_Bonus; 1915 } else { 1916 return spin_duration; 1917 } 1918 } 1919 1920 inline static int adjust_down(int spin_duration) { 1921 // TODO: Use an AIMD-like policy to adjust _SpinDuration. 1922 // AIMD is globally stable. 1923 int x = spin_duration; 1924 if (x > 0) { 1925 // Consider an AIMD scheme like: x -= (x >> 3) + 100 1926 // This is globally sample and tends to damp the response. 1927 x -= Knob_Penalty; 1928 if (x < 0) { x = 0; } 1929 return x; 1930 } else { 1931 return spin_duration; 1932 } 1933 } 1934 1935 bool ObjectMonitor::short_fixed_spin(JavaThread* current, int spin_count, bool adapt) { 1936 for (int ctr = 0; ctr < spin_count; ctr++) { 1937 TryLockResult status = TryLock(current); 1938 if (status == TryLockResult::Success) { 1939 if (adapt) { 1940 _SpinDuration = adjust_up(_SpinDuration); 1941 } 1942 return true; 1943 } else if (status == TryLockResult::Interference) { 1944 break; 1945 } 1946 SpinPause(); 1947 } 1948 return false; 1949 } 1950 1951 // Spinning: Fixed frequency (100%), vary duration 1952 bool ObjectMonitor::TrySpin(JavaThread* current) { 1953 1954 // Dumb, brutal spin. Good for comparative measurements against adaptive spinning. 1955 int knob_fixed_spin = Knob_FixedSpin; // 0 (don't spin: default), 2000 good test 1956 if (knob_fixed_spin > 0) { 1957 return short_fixed_spin(current, knob_fixed_spin, false); 1958 } 1959 1960 // Admission control - verify preconditions for spinning 1961 // 1962 // We always spin a little bit, just to prevent _SpinDuration == 0 from 1963 // becoming an absorbing state. Put another way, we spin briefly to 1964 // sample, just in case the system load, parallelism, contention, or lock 1965 // modality changed. 1966 1967 int knob_pre_spin = Knob_PreSpin; // 10 (default), 100, 1000 or 2000 1968 if (short_fixed_spin(current, knob_pre_spin, true)) { 1969 return true; 1970 } 1971 1972 // 1973 // Consider the following alternative: 1974 // Periodically set _SpinDuration = _SpinLimit and try a long/full 1975 // spin attempt. "Periodically" might mean after a tally of 1976 // the # of failed spin attempts (or iterations) reaches some threshold. 1977 // This takes us into the realm of 1-out-of-N spinning, where we 1978 // hold the duration constant but vary the frequency. 1979 1980 int ctr = _SpinDuration; 1981 if (ctr <= 0) return false; 1982 1983 // We're good to spin ... spin ingress. 1984 // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades 1985 // when preparing to LD...CAS _owner, etc and the CAS is likely 1986 // to succeed. 1987 if (_succ == nullptr) { 1988 _succ = current; 1989 } 1990 Thread* prv = nullptr; 1991 1992 // There are three ways to exit the following loop: 1993 // 1. A successful spin where this thread has acquired the lock. 1994 // 2. Spin failure with prejudice 1995 // 3. Spin failure without prejudice 1996 1997 while (--ctr >= 0) { 1998 1999 // Periodic polling -- Check for pending GC 2000 // Threads may spin while they're unsafe. 2001 // We don't want spinning threads to delay the JVM from reaching 2002 // a stop-the-world safepoint or to steal cycles from GC. 2003 // If we detect a pending safepoint we abort in order that 2004 // (a) this thread, if unsafe, doesn't delay the safepoint, and (b) 2005 // this thread, if safe, doesn't steal cycles from GC. 2006 // This is in keeping with the "no loitering in runtime" rule. 2007 // We periodically check to see if there's a safepoint pending. 2008 if ((ctr & 0xFF) == 0) { 2009 // Can't call SafepointMechanism::should_process() since that 2010 // might update the poll values and we could be in a thread_blocked 2011 // state here which is not allowed so just check the poll. 2012 if (SafepointMechanism::local_poll_armed(current)) { 2013 break; 2014 } 2015 SpinPause(); 2016 } 2017 2018 // Probe _owner with TATAS 2019 // If this thread observes the monitor transition or flicker 2020 // from locked to unlocked to locked, then the odds that this 2021 // thread will acquire the lock in this spin attempt go down 2022 // considerably. The same argument applies if the CAS fails 2023 // or if we observe _owner change from one non-null value to 2024 // another non-null value. In such cases we might abort 2025 // the spin without prejudice or apply a "penalty" to the 2026 // spin count-down variable "ctr", reducing it by 100, say. 2027 2028 JavaThread* ox = static_cast<JavaThread*>(owner_raw()); 2029 if (ox == nullptr) { 2030 ox = static_cast<JavaThread*>(try_set_owner_from(nullptr, current)); 2031 if (ox == nullptr) { 2032 // The CAS succeeded -- this thread acquired ownership 2033 // Take care of some bookkeeping to exit spin state. 2034 if (_succ == current) { 2035 _succ = nullptr; 2036 } 2037 2038 // Increase _SpinDuration : 2039 // The spin was successful (profitable) so we tend toward 2040 // longer spin attempts in the future. 2041 // CONSIDER: factor "ctr" into the _SpinDuration adjustment. 2042 // If we acquired the lock early in the spin cycle it 2043 // makes sense to increase _SpinDuration proportionally. 2044 // Note that we don't clamp SpinDuration precisely at SpinLimit. 2045 _SpinDuration = adjust_up(_SpinDuration); 2046 return true; 2047 } 2048 2049 // The CAS failed ... we can take any of the following actions: 2050 // * penalize: ctr -= CASPenalty 2051 // * exit spin with prejudice -- abort without adapting spinner 2052 // * exit spin without prejudice. 2053 // * Since CAS is high-latency, retry again immediately. 2054 break; 2055 } 2056 2057 // Did lock ownership change hands ? 2058 if (ox != prv && prv != nullptr) { 2059 break; 2060 } 2061 prv = ox; 2062 2063 if (_succ == nullptr) { 2064 _succ = current; 2065 } 2066 } 2067 2068 // Spin failed with prejudice -- reduce _SpinDuration. 2069 if (ctr < 0) { 2070 _SpinDuration = adjust_down(_SpinDuration); 2071 } 2072 2073 if (_succ == current) { 2074 _succ = nullptr; 2075 // Invariant: after setting succ=null a contending thread 2076 // must recheck-retry _owner before parking. This usually happens 2077 // in the normal usage of TrySpin(), but it's safest 2078 // to make TrySpin() as foolproof as possible. 2079 OrderAccess::fence(); 2080 if (TryLock(current) == TryLockResult::Success) { 2081 return true; 2082 } 2083 } 2084 2085 return false; 2086 } 2087 2088 2089 // ----------------------------------------------------------------------------- 2090 // WaitSet management ... 2091 2092 ObjectWaiter::ObjectWaiter(JavaThread* current) { 2093 _next = nullptr; 2094 _prev = nullptr; 2095 _notified = 0; 2096 _notifier_tid = 0; 2097 TState = TS_RUN; 2098 _thread = current; 2099 _event = _thread->_ParkEvent; 2100 _active = false; 2101 assert(_event != nullptr, "invariant"); 2102 } 2103 2104 void ObjectWaiter::wait_reenter_begin(ObjectMonitor * const mon) { 2105 _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(_thread, mon); 2106 } 2107 2108 void ObjectWaiter::wait_reenter_end(ObjectMonitor * const mon) { 2109 JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(_thread, _active); 2110 } 2111 2112 inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) { 2113 assert(node != nullptr, "should not add null node"); 2114 assert(node->_prev == nullptr, "node already in list"); 2115 assert(node->_next == nullptr, "node already in list"); 2116 // put node at end of queue (circular doubly linked list) 2117 if (_WaitSet == nullptr) { 2118 _WaitSet = node; 2119 node->_prev = node; 2120 node->_next = node; 2121 } else { 2122 ObjectWaiter* head = _WaitSet; 2123 ObjectWaiter* tail = head->_prev; 2124 assert(tail->_next == head, "invariant check"); 2125 tail->_next = node; 2126 head->_prev = node; 2127 node->_next = head; 2128 node->_prev = tail; 2129 } 2130 } 2131 2132 inline ObjectWaiter* ObjectMonitor::DequeueWaiter() { 2133 // dequeue the very first waiter 2134 ObjectWaiter* waiter = _WaitSet; 2135 if (waiter) { 2136 DequeueSpecificWaiter(waiter); 2137 } 2138 return waiter; 2139 } 2140 2141 inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) { 2142 assert(node != nullptr, "should not dequeue nullptr node"); 2143 assert(node->_prev != nullptr, "node already removed from list"); 2144 assert(node->_next != nullptr, "node already removed from list"); 2145 // when the waiter has woken up because of interrupt, 2146 // timeout or other spurious wake-up, dequeue the 2147 // waiter from waiting list 2148 ObjectWaiter* next = node->_next; 2149 if (next == node) { 2150 assert(node->_prev == node, "invariant check"); 2151 _WaitSet = nullptr; 2152 } else { 2153 ObjectWaiter* prev = node->_prev; 2154 assert(prev->_next == node, "invariant check"); 2155 assert(next->_prev == node, "invariant check"); 2156 next->_prev = prev; 2157 prev->_next = next; 2158 if (_WaitSet == node) { 2159 _WaitSet = next; 2160 } 2161 } 2162 node->_next = nullptr; 2163 node->_prev = nullptr; 2164 } 2165 2166 // ----------------------------------------------------------------------------- 2167 // PerfData support 2168 PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts = nullptr; 2169 PerfCounter * ObjectMonitor::_sync_FutileWakeups = nullptr; 2170 PerfCounter * ObjectMonitor::_sync_Parks = nullptr; 2171 PerfCounter * ObjectMonitor::_sync_Notifications = nullptr; 2172 PerfCounter * ObjectMonitor::_sync_Inflations = nullptr; 2173 PerfCounter * ObjectMonitor::_sync_Deflations = nullptr; 2174 PerfLongVariable * ObjectMonitor::_sync_MonExtant = nullptr; 2175 2176 // One-shot global initialization for the sync subsystem. 2177 // We could also defer initialization and initialize on-demand 2178 // the first time we call ObjectSynchronizer::inflate(). 2179 // Initialization would be protected - like so many things - by 2180 // the MonitorCache_lock. 2181 2182 void ObjectMonitor::Initialize() { 2183 assert(!InitDone, "invariant"); 2184 2185 if (!os::is_MP()) { 2186 Knob_SpinLimit = 0; 2187 Knob_PreSpin = 0; 2188 Knob_FixedSpin = -1; 2189 } 2190 2191 if (UsePerfData) { 2192 EXCEPTION_MARK; 2193 #define NEWPERFCOUNTER(n) \ 2194 { \ 2195 n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events, \ 2196 CHECK); \ 2197 } 2198 #define NEWPERFVARIABLE(n) \ 2199 { \ 2200 n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events, \ 2201 CHECK); \ 2202 } 2203 NEWPERFCOUNTER(_sync_Inflations); 2204 NEWPERFCOUNTER(_sync_Deflations); 2205 NEWPERFCOUNTER(_sync_ContendedLockAttempts); 2206 NEWPERFCOUNTER(_sync_FutileWakeups); 2207 NEWPERFCOUNTER(_sync_Parks); 2208 NEWPERFCOUNTER(_sync_Notifications); 2209 NEWPERFVARIABLE(_sync_MonExtant); 2210 #undef NEWPERFCOUNTER 2211 #undef NEWPERFVARIABLE 2212 } 2213 2214 _oop_storage = OopStorageSet::create_weak("ObjectSynchronizer Weak", mtSynchronizer); 2215 2216 DEBUG_ONLY(InitDone = true;) 2217 } 2218 2219 void ObjectMonitor::print_on(outputStream* st) const { 2220 // The minimal things to print for markWord printing, more can be added for debugging and logging. 2221 st->print("{contentions=0x%08x,waiters=0x%08x" 2222 ",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}", 2223 contentions(), waiters(), recursions(), 2224 p2i(owner())); 2225 } 2226 void ObjectMonitor::print() const { print_on(tty); } 2227 2228 #ifdef ASSERT 2229 // Print the ObjectMonitor like a debugger would: 2230 // 2231 // (ObjectMonitor) 0x00007fdfb6012e40 = { 2232 // _metadata = 0x0000000000000001 2233 // _object = 0x000000070ff45fd0 2234 // _pad_buf0 = { 2235 // [0] = '\0' 2236 // ... 2237 // [43] = '\0' 2238 // } 2239 // _owner = 0x0000000000000000 2240 // _previous_owner_tid = 0 2241 // _pad_buf1 = { 2242 // [0] = '\0' 2243 // ... 2244 // [47] = '\0' 2245 // } 2246 // _next_om = 0x0000000000000000 2247 // _recursions = 0 2248 // _EntryList = 0x0000000000000000 2249 // _cxq = 0x0000000000000000 2250 // _succ = 0x0000000000000000 2251 // _Responsible = 0x0000000000000000 2252 // _SpinDuration = 5000 2253 // _contentions = 0 2254 // _WaitSet = 0x0000700009756248 2255 // _waiters = 1 2256 // _WaitSetLock = 0 2257 // } 2258 // 2259 void ObjectMonitor::print_debug_style_on(outputStream* st) const { 2260 st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this)); 2261 st->print_cr(" _metadata = " INTPTR_FORMAT, _metadata); 2262 st->print_cr(" _object = " INTPTR_FORMAT, p2i(object_peek())); 2263 st->print_cr(" _pad_buf0 = {"); 2264 st->print_cr(" [0] = '\\0'"); 2265 st->print_cr(" ..."); 2266 st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1); 2267 st->print_cr(" }"); 2268 st->print_cr(" _owner = " INTPTR_FORMAT, p2i(owner_raw())); 2269 st->print_cr(" _previous_owner_tid = " UINT64_FORMAT, _previous_owner_tid); 2270 st->print_cr(" _pad_buf1 = {"); 2271 st->print_cr(" [0] = '\\0'"); 2272 st->print_cr(" ..."); 2273 st->print_cr(" [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1); 2274 st->print_cr(" }"); 2275 st->print_cr(" _next_om = " INTPTR_FORMAT, p2i(next_om())); 2276 st->print_cr(" _recursions = " INTX_FORMAT, _recursions); 2277 st->print_cr(" _EntryList = " INTPTR_FORMAT, p2i(_EntryList)); 2278 st->print_cr(" _cxq = " INTPTR_FORMAT, p2i(_cxq)); 2279 st->print_cr(" _succ = " INTPTR_FORMAT, p2i(_succ)); 2280 st->print_cr(" _Responsible = " INTPTR_FORMAT, p2i(_Responsible)); 2281 st->print_cr(" _SpinDuration = %d", _SpinDuration); 2282 st->print_cr(" _contentions = %d", contentions()); 2283 st->print_cr(" _WaitSet = " INTPTR_FORMAT, p2i(_WaitSet)); 2284 st->print_cr(" _waiters = %d", _waiters); 2285 st->print_cr(" _WaitSetLock = %d", _WaitSetLock); 2286 st->print_cr("}"); 2287 } 2288 #endif --- EOF ---